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Click on the New Padlet button in the top right corner.
Enter in a Title, Description, and select the Layout. The freeform layout allows you to move posts around and usually works best for brainstorming activities.
Once you're done, click the Next button.
The default sharing options will allow anyone who has a link to the Padlet to write to it, but only you will be able to moderate posts (move, delete). This is usually what is wanted.
Click the Next button again and then click the Start Posting button.